The broad, long-term objective is to characterize phosphatidylethanolamine (PE) at the luminal endothelial surface, and develop new biomarkers for vascular health and diseases. Accumulating evidence from past decades demonstrates that PE is an important anticoagulant. However, the distribution and dynamics of PE at the blood-endothelium interface remain virtually unknown due to a lack of investigative probes. Recently, we developed PE-specific molecular probes derived from Duramycin, which bind PE with high affinity and high specificity. Using these probes, important preliminary data were obtained in support of the current project. First, we discovered an extraordinarily high level of PE at the luminal endothelial surface of aortic flow dividers and along the ascending aorta. Second, these vascular regions are also the primary targets for anti-PE (aPE) autoimmunity, providing a physical link between aPE and idiopathic thrombosis. In addition, cultured endothelial cells upregulate surface PE when subject to shear stress, thereby suggesting a flow-mediated regulatory mechanism. Furthermore, we documented that PE at the blood-endothelium interface is severely suppressed in hypertensive, as opposed to normotensive, vessels. In light of the preliminary data, the primary goal of this project is to better characterize vascular PE. Four Specific Aims are proposed to: 1) Synthesize and characterize Duramycin-derived PE-specific molecular probes, in particular, the gadolinium-labeled T1 agents for high-resolution, target-specific MRI. 2) Explore the mechanism of flow-mediated PE upregulation in endothelial cells, where we hypothesize that the modulation of surface PE is governed by a mechanotransduction process in response to shear stress. 3) Determine the normal distribution profile of vascular PE on a tissue level using target-specific MRI; we hypothesize that the level of PE at the luminal endothelial surface correlates with the degree of hemodynamic stress. 4) Characterize PE in hypertensive vasculature using various rat models of hypertension and in response to antihypertensive therapies. We hypothesize that the vascular PE is a marker for endothelial dysfunction associated with hypertension. Overall, new knowledge about PE at the blood-endothelium interface will enhance our understanding of the regulation and impairment of hemostasis. In turn, these discoveries regarding the dynamics of vascular PE will give rise to new biomarkers for endothelial health, and the progression and treatments of vascular anomalies. RELEVANCE TO PUBLIC HEALTH The characterization of PE, as a critical anticoagulant in the vasculature, will help us understand the modulation of the thrombotic potential of the circulating blood by the endothelium. The dynamics of vascular PE will provide important information regarding the thrombotic disorders and endothelial dysfunction in vascular diseases.